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1003.2-1992, section 5.22.3 (patch), page 585, lines 3483-
3489 says
"-o outfile Instead of modifying the files (specified by the file
operand or the diff listings) directly, write a
copy of the file referenced by each patch, with the appropriate
differences applied, to outfile. Multiple
patches for a single file shall be applied to the intermediate
versions of the file created by any previous
patches and shall result in multiple, concatenated versions of the
file being written to outfile."
This does not describe historical practice.

Historical practice has
been to override just the first occurance
of the first file in the patch file.
The rationale for patch contains a number of changes that were
made from historical practice but this is not
mentioned. Moreover, the change is significant, unintuative and
likely to cause problems for people
expecting the historical behaviour.
Was this change from historical practice intentional?

Interpretation Response
The standard clearly states the requirements for patch -o and
conforming implementations must conform
to this.
It is true that historical versions of patch only wrote the changes
that would be made by the first chunk of a
patch file to the file specified by the -o outfile option. The working
group believed that you could have a
security issue of overwriting files unintentionally when a patch file
contained multiple chunks, and the
historic documentation never indicated that this only applied to
the first chunk.
This was thus an intentional change.
Issues concerning the wording of the rationale have been
forwarded to the sponsor, but these would not
result in a normative change.